Know your limit
...a white circle with a black diagonal across it.
You certainly need a masters degree in advanced semiotics to work out what it means - technically “national speed limits apply”. This is the most stupid and unhelpful sign on our roads. It should be scrapped.
But you can't replace it with one that just says 60 or 70 - because if you towing a trailer, or you are in a van or an articulated lorry the national speed limit isn't that. And that is why lorries hold you up as you speed off on holiday.